constify RHash::ifnone.

RHash::ifnone should be protected by write-barriers so this field
should be const. However, to introduce GC.compact, the const was
removed. This commit revert this removing `const` and modify
gc.c `TYPED_UPDATE_IF_MOVED` to remove `const` forcely by a type cast.

2 files changed, 2 insertions, 2 deletions

diff --git a/gc.c b/gc.c
index 1c2959cbad..feea9852ec 100644
--- a/gc.c
+++ b/gc.c
@@ -915,7 +915,7 @@ static inline void gc_prof_set_heap_info(rb_objspace_t *);
 
 #define TYPED_UPDATE_IF_MOVED(_objspace, _type, _thing) do { \
     if (gc_object_moved_p(_objspace, (VALUE)_thing)) { \
-       (_thing) = (_type)RMOVED((_thing))->destination; \
+       *((_type *)(&_thing)) = (_type)RMOVED((_thing))->destination; \
     } \
 } while (0)
 
diff --git a/internal.h b/internal.h
index b931c115df..f8baba48c1 100644
--- a/internal.h
+++ b/internal.h
@@ -873,7 +873,7 @@ struct RHash {
         struct ar_table_struct *ar; /* possibly 0 */
     } as;
     int iter_lev;
-    VALUE ifnone;
+    const VALUE ifnone;
 };
 
 #ifdef RHASH_ITER_LEV